The present invention relates to a gas discharge panel which is used for display of images with a computer, television or other device, and a method of production for such a panel. More particularly, the present invention relates to a gas discharge panel which has discharge cells arranged in a matrix layout.
Recently, gas discharge panels have received attention as a flat-type display for computers, televisions, and other such devices.
Gas discharge panels are categorized broadly as direct-current type (DC type) or alternating-current type (AC type), and at present the AC type, which is suitable for large screens, is the mainstream choice.
In an AC-type gas discharge panel, a discharge cell is illuminated by applying an alternating current pulse to an electrode, which is coated with a dielectric layer to maintain discharge. Two kinds are known, a surface discharge type, which has sustaining electrode pairs arranged in parallel on the front panel side, and an opposed discharge type, which has sustaining electrode pairs arranged in opposition to each other on the front panel and back panel.
FIG. 15 shows an example of a conventional AC plane discharge type gas discharge panel.
This gas discharge panel has a front panel 110 and a back panel arranged opposite each other, sealed around the outer edge with a sealing material composed of low-melting glass to form the gas discharge space. The airtight space 104 formed between the two substrates is filled with an. inert gas (a mixture of helium and xenon) at a pressure of about 300 Torr to 500 Torr (40 kPa to 66.5 kPa).
The front panel 110 has display electrode pairs 112a, 112b, formed on the opposing face (the side facing the back panel), and has a dielectric layer 113, composed of dielectric glass, and a protective layer 114, composed of MgO, formed as a coating over the electrodes.
The back panel 120 has address electrodes 122 patterned on the opposing face (the side facing the front panel), and has a back dielectric layer 123 formed as a coating over the electrodes. Barrier ribs 124 are formed on top of the back dielectric layer 123, and RGB phosphor layers 131 are formed between adjacent barrier ribs 124.
The space 140 delimited by the barrier ribs 124 becomes the light-emitting area (discharge cells), and a phosphor layer is applied to each discharge cell. The barrier ribs 124 and address electrodes 122 are formed in the same direction, and the display electrode pairs 112a, 112b, are perpendicular to the address electrodes 122.
In this gas discharge panel, after applying an address pulse between the address electrode 122 and the display electrode 112a, based on the image data to be displayed, applies a sustaining pulse to the pair formed by the display electrode 112a and display electrode 112b, thereby selectively causing a sustaining discharge in the discharge cell. In the discharge cell subject to sustaining discharge, ultraviolet rays are produced, visible light is generated and emitted from the RGB-colored phosphor layers 131, and an image is displayed.
Here, the barrier ribs 124 divide the discharge space into discharge cells, preventing cross-talk (the phenomenon of discharge mixing across the interface of discharge cells).
Since the filling pressure of discharge gas is usually lower than atmospheric pressure, the front glass substrate 111 and back glass substrate 121 are pressed inward by atmospheric pressure. Here, the barrier ribs 124 act as a spacer, maintaining the space between the two substrates, with the peaks of the barrier ribs contacting the inner surface of the front panel 110.
The following describes a production method for the above gas discharge panel.
For the front panel 110, display electrodes 112a, 112b, are formed on the front glass substrate 111, a dielectric layer 113 is formed by applying and baking a layer of dielectric glass covering the electrodes, and a protective layer 114 is formed by EB evaporation of MgO over the dielectric layer 113.
For the back panel 120, address electrodes 122 are formed on the back glass substrate 121, the back dielectric layer 123 is formed covering the electrodes, and barrier ribs 124 are formed on top of the back dielectric layer 123.
The barrier ribs 124 may be, for example, formed on the surface of the back dielectric layer 123, then coated with resist. Next, the resist coating may be patterned in stripes, the unnecessary portion of barrier rib material removed by sand blasting, and the coating then baked.
Next, between barrier ribs 124, a phosphor paste is potted by printing or other method and baked to form a phosphor layer 131. This completes production of the back panel 120.
The front panel 110 and back panel 120, produced as described above, have a low-melting glass applied as a sealing material around their outer edges, are stacked and sealed by baking, then evacuated and the space between the two panels is filled with an inert gas, completing production of the gas discharge panel.
In this gas discharge panel, it is desirable for color images to be displayed accurately, and for production cost to be low.
It should be noted that the illumination strength of each discharge cell is affected by the shape of the cell. In order to accurately display color images, it is necessary for the discharge cells which are arranged in a matrix to have a uniform shape. This means that it is necessary for the barrier ribs to have uniform height and width. However, if baking occurs after the barrier rib material is applied and coated, the coating will shrink during baking. This causes difficulty in maintaining a uniform height of the barrier ribs and reduces yield. This in turn increases the production cost of gas discharge panels.
It is therefore an object of the present invention to provide a gas discharge panel which has precise color display and is easily manufactured.
To this end, the gas discharge panel has a first and a second substrate facing each other with a space in between, the space filled with discharge gas to form a discharge space. At least one of the first and second substrates has groups of electrode pairs for sustaining discharge arranged on its surface. The first substrate has phosphor layers arranged on it, such that a plurality of discharge cells is formed in a matrix pattern along the groups of electrode pairs. A gas discharge panel which displays images by selectively illuminating a plurality of discharge cells, incorporates gap members of a certain shape between the first and second substrates, in areas corresponding to the borders between discharge cells, except for the center of the discharge cell. Here, a certain shape means the gap members have a particular shape, such as spherical or rod-shaped, and their shape does not change over the process of panel production, i.e., the gap members do not deform during baking as a paste material does.
According to the present invention, even without forming barrier ribs between the front panel and back panel, the spacing (gap) between the substrates can be precisely prescribed. Also, since the gap members are not placed in the central area of the discharge cells, the gap members do not hinder discharge, and the panel is resistant to discharge failure.
Therefore, it is easier to produce a gas discharge panel which is capable of high-precision image display, at a lower cost than heretofore.
This type of gas discharge panel can be realized through the following processes: (a) a process for arranging a phosphor layer, which corresponds to the illumination color of the discharge cell, in the desired place on one substrate; (b) a a process for affixing gap members of a certain shape on one substrate in a position which corresponds to the border region between discharge cells; and (c) a process for stacking the second substrate on the substrate with the gap members affixed and joining the two substrates.
Here, when forming phosphor layers corresponding to the illumination color of each discharge cell in this way without forming barrier ribs, the conventional method of applying a phosphor paste is prone to cause mixing of colors between adjacent phosphor layers. However, by using a method such as pasting a film containing the phosphor element on to the substrate and patterning, it is possible to successfully form phosphor layers on the substrate, which correspond to the illumination color of each discharge cell.
It is common to use a material such as glass beads to form the gap members, but in this case it is impossible to divide the discharge cells as with barrier ribs, tending to create the problem of cross-talk. Then, when cross-talk occurs, the illumination color of one discharge cell mixes with the illumination color of an adjacent discharge cell, causing a reduction in illumination color quality.
In contrast, cross-talk can be prevented if the groups of electrode pairs and their surrounding structures are arranged such that discharge occurs primarily towards the center of each discharge cell, away from the edges of the discharge cells.
The method of simply arranging gap members on one substrate and joining it with another substrate creates a tendency to have gap members in the center of the discharge cells. The gap members in the center of the discharge cells creates a problem of hindering discharge.
Here, a scheme is necessary to arrange the gap members in the areas of the substrate which correspond to the edges of the discharge cells, and avoid the central areas.
To this end, effective techniques include, for example, forming an adhesive layer in advance in the areas corresponding to edges, or reducing the thickness of the phosphor layer in the areas corresponding to edges.
The stated objective is achieved also by setting filling pressure of the discharge gas in proximity to atmospheric pressure (within a range of 80% to 120% of atmospheric pressure).
That is, setting filling pressure of the discharge gas in proximity to atmospheric pressure avoids influence of atmospheric pressure on the substrates. This means that in the display area, even in an area which is not in contact (this is an area which is not in contact across a plurality of cells in the vertical or horizontal direction, implying a somewhat broad area) across a plurality of discharge cells in two dimensions, the proper gap can be maintained between the two substrates.
By this method, even with a very small amount of distributed gap members, the gap between the substrates can be properly maintained, simplifying production of gas discharge panels compared to conventional methods. Also, it is possible to maintain the proper gap between the two substrates without any gap members in the image display area at all.
The stated objective is achieved also in production of gas discharge panels by using (a) a method of mixing gap members in when forming the phosphor layer, and (b) a method of mixing gap members in when forming the dielectric layer. These methods allow the space between the front panel and back panel to be precisely prescribed, and, since it is not necessary to form barrier ribs, also allow the stated objective to be achieved.